1. Field of the Invention
This invention relates to a battery voltage discriminator circuit for use in an electronic apparatus such as a portable word processor, and more particularly to a battery voltage discriminator circuit for determining whether or not the battery has been consumed to the extent that it is no longer able to normally drive the apparatus.
2. Description of the Prior Art
A conventional battery voltage discriminator circuit provided in such an electronic apparatus using a battery as a drive power source is usually arranged as shown in FIG. 7. The terminal voltage V.sub.B of a battery B.sub.a which is used as a drive power source is converted by a DC--DC converter PS into a constant voltage adjusted to a predetermined load voltage V.sub.C which is in turn supplied to a load L.sub.O. The battery voltage V.sub.B is divided by two resistors R.sub.1 and R.sub.2 to generate a detection battery voltage V.sub.1 the level of which corresponds to that of the battery voltage V.sub.B as shown in (a) of FIG. 8. The detection battery voltage V.sub.1 is inputted to an inverting input terminal of a comparator CP. The load voltage V.sub.C is divided by two resistors R.sub.3 and R.sub.4 to generate a predetermined reference voltage V.sub.2 which is input to a non-inverting input terminal of the comparator CP. When the detection battery voltage V.sub.1 drops to the reference voltage V.sub. 2, the output terminal of the comparator CP becomes high to output an abnormal voltage detection signal LB as shown in (b) of FIG. 8, so that an alarm is given to indicate that the battery B.sub.a has been consumed to the extent that it is no longer available for use. In FIG. 7, capacitors C.sub.1 and C.sub.2 are provided for eliminating ripples from the battery voltage V.sub.B and the load voltage V.sub.C.
The case will be considered in which the circuit of FIG. 7 is applied to a portable computer or word processor having a variety of loads such as a printer, a modem, a buzzer, an LED indicator or the like. When any abrupt change in load occurs as in the starting of an X-directional drive motor for the printer or on the connection of the modem to a communication line, there may occur an overcurrent flowing to cause a drop in the battery voltage V.sub.B and a momentary sudden drop in the detection battery voltage V.sub.1 to a lower voltage level than the reference voltage V.sub.2, with the result that an abnormal voltage detection signal LB is produced despite the fact that the battery B.sub.a has not been consumed to the extent of being no longer available for use.
In order to obviate such inconvenience, measures have been taken such that when an abnormal voltage detection signal is output upon the occurrence of any abrupt load fluctuations, no alarm of such occurrence is given, or such that the detection conditions for battery consumption detection are set to comply the maximum conceivable load condition in which, for example, the printer prints black on the entire surface of a recording paper sheet.
However, these measures have been found unsatisfactory. With the first mentioned measure, it is impossible to accurately detect, as originally intended thereby, that the battery voltage has dropped to the extent that it is no longer available for driving the apparatus. With the latter measure in which, even when the load condition is low, the degree of battery consumption is determined according to detection conditions corresponding to the maximum possible load condition, it is likely that an abnormal voltage detection signal will be erroneously produced even if the battery is still available for effective use. Therefore, the latter measure permits no efficient use of the battery, which is disadvantageous from the standpoint of economy.